Spandex fibers are polyurethane/urea fibers composed of molecular chains which have hard and soft segments. The fibers are elastomeric and have very high extensibility to break (400% to 800%). The fibers also have high recovery from stretching. Spandex fibers are stronger and lighter than rubber. The fibers, which are white and dyeable, can be drawn (stretched) during or subsequent to spinning. Mono-filaments are obtained from a spinneret with a single hole.
In prior art processes, the manufacture of elastomeric threads for textile uses has been achieved by reacting glycols of polyethers or polyesters with organic diisocyanates to make polyurethane pre-polymers having residual isocyanate groups located on most of the pre-polymer ends. The polyurethane pre-polymers are dissolved in solvents to give a 25% to 40% solids solution with a controlled viscosity. The mixture of pre-polymer and solvent is then contacted with an organic diamine and optionally, a small amount of secondary amine to obtain large molecules of elastomer in solution. Filaments are formed by evaporating the solvent (dry spinning) or by coagulation (wet spinning).
Prior art processes are limited by the need for producing pre-polymers which are soluble in some organic solvent to an extent of greater than 15% solids. Only certain diisocyanates can therefore be employed for reaction with glycols of polyethers or polyesters. Some diisocyanates which produce superior resistance to sunlight or to harsh chemicals such as chlorine cannot be employed because they yield unsuitable pre-polymers, i.e., pre-polymers not soluble in liquids for reaction with diamines, or the reaction product with diamines is insoluble.
Prior art processes require addition of solvent in order to keep the viscosity of the elastomer low enough for spinning through small spinneret holes. The use of solvent requires high energy costs for solvent removal, recovery and purification.
Prior art processes such as dry spinning have speeds that are dependent on rate of solvent removal. Speeds are carefully regulated to keep filaments from sticking together, or to provide sticking of tiny filaments in immediate proximity of each other to form high denier fibers at high spinning speed. When several threads are produced in the same spinning cell, a problem arises relating to adjacent threads sticking together.
Prior art processes involving wet spinning include relatively slow spinning speeds of about 50 meters/minute and produce elastomeric threads having poor physical properties due in part to lack of a high degree of orientation of elastomeric molecules. In addition, the elastomeric products must be "heat set", which is an expensive and inconsistent process
U.S. Pat. No. 2,935,372 (Steuber) relates to a process for preparing fibers and filaments by extruding an intermediate macromolecular composition through an orifice blanketed by an inert gas and into the vapors of a monomeric intermediate. The macromolecular intermediate can be an isocyanate-terminated polyalkylene oxide (column 2, lines 30-75) and the monomeric intermediate can be ethylenediamine. The concentration of the diamine is about 1000 ppm The solid filament is wound up at speeds of about 50 to 175 y.p.m. (yards per minute) to obtain a product having a low tenacity of 0.2 grams per denier, an elongation of 500% and a 94% recovery from tensile elongation. Also disclosed is a cross flow of inert gas at the face of the spinneret to prevent reaction immediately contiguous to the spinneret face (column 6, line 66). The fibers which are produced have a uniform cross-section (page 8, line 34). Also, a delicate balance of reactant materials is not maintained (page 8, line 54).
U.S. Pat. No. 3,115,384 (Cacella et al.) relates to a method of making a filament comprising contacting a liquid polyurethane prepolymer having terminal isocyanate groups with a primary aliphatic diamine in a setting bath complete with hydroxyl-containing solvent to effect a setting to the solid state of the external surface only of the liquid prepolymer. The interior of the filament which remains fluid is then treated under anhydrous conditions and at a specified temperature to effect setting to a solid state.
U.S. Pat. No. 3,666,708 (Nakahara et al.) relates to a method of preparing a chain-extended polyurethane from a prepolymer having terminal isocyanate groups, a bi-functional chain-extending agent and N,N-dialkylalkylene diamine.
U.S. Pat. No. 3,753,953 (Jan Leenwerik et al.) relates to a method of preparing a polyurethane elastomer comprising reacting a diisocyanate with a polyester to obtain a polyurethane prepolymer, and subsequently reacting the polyurethane prepolymer with a diamine chain extender. The reaction of prepolymer with chain extender takes place in an aprotic polar solvent such as dimethyl formamide and the like.
In spinning from solvents, physical properties change with different spinning speeds. In the disclosed solventless process, spinning speeds can vary over a wide range without changing the physical properties of the fiber. Physical properties of the fiber prepared according to the present process can be changed simply by changing the concentration of the diamine in the inert gas surrounding the prepolymer in the spinning tower.